The use of pavement markings to guide and direct motorists traveling along a roadway is well known. Pavement markings are typically retroreflective so motorists can see the markings at night. Retroreflection describes the mechanism where light incident on a surface is reflected so that much of the incident beam is directed back toward its source. A common retroreflective pavement marking comprises glass or glass-ceramic microspheres partially embedded in a pigmented paint. When the surface of the pavement marking becomes wet, the microspheres become coated with water, which in turn reduces the retroreflection.
Various retroreflective elements or aggregates have been described in the art for use in pavement markings.
For example, U.S. Pat. No. 3,418,896 (abstract) describes reflective elements which are flat on their upper and lower surfaces and which have vertical side walls covered by a plurality of small glass spheres partially embedded in the vertical side walls, the width of the flat surfaces being at least twice the thickness of the elements and the thickness being in the order of ⅛-½″ and the width not exceeding 1″. The reflective elements can be incorporated into reflective markers for improved nighttime retroreflectivity especially in rainy weather. The elements can be incorporated into a hot-sprayed liquid binder that is solvent-free.
As another example, U.S. Pat. No. 5,750,191 describes a process and retroreflective elements are provided. The process of preparing a retroreflective element includes the steps of (a) combining a bed of optical elements and one or more core elements comprising a thermoplastic material; and (b) agitating the combination of optical elements and core elements for a sufficient period of time and at a sufficient temperature to coat the optical elements onto the core elements to form retroreflective elements.
As another example, U.S. Pat. No. 6,247,818 teaches a method for making retroreflective elements that are retroreflective under dry and-or wet conditions. The method provides a means for placing optical elements and/or skid-resistant particles on selected surfaces.
Although various retroreflective elements have been identified, industry would find advantage in alternative retroreflective elements having improved manufacturing efficiency and/or improved performance.